Lubricating grease thickened with indigo and soap mixture



3,009,879 LUBRICATING GREASE TIHCKENED WITH INDIGO AND SOAP MIXTURE James R. Roach, Beacon, N.Y., assignor to Texaco Inc, a corporation of Delaware No Drawing. Filed Oct. 1, 1957, Scr. No. 687,348 8 Claims. (Cl. 252-42.1)

This invention relates to lubricating greases thickened with indigo in combination with mixtures of sodium or lithium soaps of different types.

It has been found heretofore by John P. Dilworth and James R. Roach, as disclosed in their US. Patent 2,791,- 560, that the combination of finely divided indigo and a sodium or lithium soap of a fatty acid containing from 12 to 16 carbon atoms permolecule as a grease thickening agent produces greases having very outstanding high temperature performance properties, which are greatly superior to those obtainable by employing either indigo or a fatty acid soap as the sole thickening agent. By means of this combination of thickening agents in a high molecular weight synthetic diester as the oil component, Dilworth et al. obtained very superior greases which are suitable for lubricating ball and roller bearings at elevated temperatures up to about 400 F., under service conditions involving relatively high rates of shearing. However, greases are not obtainable from mineral oils as the sole or principal oil component which are suitable for use at temperatures substantially above 300 F. by employing this combination of thickening agents.

It is now found, in accordance with the present invention, that mineral oil base greases having high temperature performance properties suitable for use at elevated temperatures in the range up to about 400 F. are obtained by employing a combination of thickening agents comprising finely divided indigo and a soap mixture of the type described by A. I. Morway and L. A. Mikeska in U.S. 2,694,683, comprising substantial amounts of both a salt of pectic acid and a salt of a lower fatty acid containing from 1 to 5 carbon atoms per molecule in combination with a soap of the type employed by Dilworth et al. The greatly improved high temperature performance properties of these greases as compared with those of mineral oil base greases thickened with the indigo and soap combination of Dilworth et al. was unexpected, since it is contrary to the experience with greases thickened with fatty acid soaps alone, wherein lower fatty acid salts employed in admixture with conventional fatty acid soaps have been found to deteriorate high temperature performance properties.

The grease compositions of this invention comprise a mineral lubricating oil as the chief oleaginous component thickened to a grease consistency with about 5 to 20 percent by weight, based on the weight of the composition, of finely divided indigo, preferably having a particle size below about one micron, in diameter, and about 5 to 20 percent by weight, based on the weight of the composition, of a mixture comprising sodium or lithium soaps of a relatively high molecular weight fatty acid, and sodium or lithium salts of pectic acid and a low molecular weight fatty acid. The relatively high molecular weight fatty acid soaps are sodium and lithium soaps of fatty acids having from 12 to 16 carbon atoms per molecule, such as for example, sodium laurate, lithium laurate, sodium myristate, lithium myristate, sodium palmitate, etc., as well as mixtures of such soaps. The preferred soaps of this character are sodium and lithium soaps of fatty acids containing at least a predominant proportion of myristic acid. The low molecular weight fatty acid salts are sodium and lithium salts of fatty acids having from 1 to 5 carbon atoms per molecule, such as sodium formate, lithium formate, sodium acetate, lithium acetate, sodium Eatented Nov. 21, 1961 propionate, lithium propionate, sodium butyrate, etc. The preferred low molecular weight fatty acid salts are sodium and lithium formates and acetates. A compound or mixture of compounds of each of the above types is present in the grease in an amount corresponding to a ratio of from about 1:3 to 3:1 with a compound or mixture of compounds of each of the other types. Preferably, the compounds or mixtures of compounds of each type are present in ratios from about 1:2 to about 2:1 with the compounds or mixtures of compounds of each of the other types. The total soap and organic acid salt content of the grease is preferably in a proportion of from about 1:2 to about 2:1 by weight with the indigo.

The mineral lubricating oil employed may be any mineral oil fraction in general in the lubricating oil viscosity range, obtained by the usual refining methods, and may be either predominantly par'alfinic or predominantly naphthenic in character. The preferred oils are refined distillate or residual fractions having viscosities in the range from about secondsSaybolt Universal at 100 F. to about 200 seconds Saybolt Universal at 210 F., or blends of such oils.

Additives of the usual types may be employed, such as oxidation inhibitors, corrosion inhibitors, tackiness agents, extreme pressure agents, and so forth. An oxidation inhibitor is preferably employed which may suitably be an inhibitor of the amine type, such as diphenylamine, alphanaphthylarnine, beta-naphthylamine, para-phenylenediamine and N,Ndiphenyl para-phenylenediamine. A compound of this type may be present in amounts from about 0.05 percent to about 5 percent by weight, and preferably from about 0.5 percent to about 2.0 percent, based on the weight of the composition. Very advantageously, the inhibitor combination described in-U.S. 2,663,691, consisting of N,Ndiphenyl para-phenylenediamine dissolved in about three times its weight of tricresyl phosphate, may be employed in these compositions. In addition, small amounts of other thickening agents which do not impair the high temperature performance properties of the grease may also be employed. Especially suitable materials of this character are estolides of hydroxy faty acids, containing from about 12 to 24 carbon atoms per molecule. The grease may suitably contain from about 0.05 percent to about 5 percent by weight of such estolide having a molecular weight in the range fromabout 800 to about 1,200, either saponified or unsaponified.

The preparation of these greases may be carried out by any convenient method, such as by merely mixing the preformed soaps, salts and indigo in suitable amounts with a mineral lubricating oil. It may be carried out very advantageously by saponification in situ of a mixture of the acids or their glycerides, preferably in the presence of a naphthenic oil and then mixing in additional mineral lubricating oil and any additives employed during cooling. The indigo may be mixed in following the saponification, or the soap and salt thickened grease may be mixed in suitable proportions with an indigo thickened grease. A small excess of sodium or lithium base may be' employed inthe saponification; for example the finished grease may suitably contain about 0.020.2 percent of free alkali (calculated as sodium or lithium hydroxide). However, this is not an essential condition, and the grease may be neutral or even slightly acid if desired.

As an example of a grease composition of this invention, a grease was prepared comprising a mineral lubricating oil thickened by 9.9 percent by weight of indigo and 10 percent by weight of a mixture of sodium salts of myristic, pectic and acetic acids in a mol ratio of l:1.2:1.5, respectively. The grease also contained 1.0 percent by weight of N,N'diphenyl para-phenylenediamine and 3.0 percent by weight of tricresyl phosphate.

The grease preparation was carried out in the following manner: A mixed soap base was prepared by saponifying a mixture of 57.5 grams of a commercial myristic acid having a saponification number of 246 and a titer of 49.8 C., 52.5 grams of a commercial pectic acid having a neutralization number of 200 and a saponification number of 319, 24 grams of acetic acid, and 15.5 grams of a 12-hydroxystearic acid estolide having a molecular weight of about 1000, in the presence of 135 grams of a refined naphthenic distillate oil having a Saybolt Universal viscosity of about 330 seconds at 100 F. The saponification was carried out by adding 78 grams of 51.8 percent aqueous sodium hydroxide to the above mixture and heating the saponification mass at 150 F. for one hour. The mass was then heated to 320 F. and maintained at that temperature for one hour with continuous stirring while 154 grams of a commercial dye grade indigo in the form of a powder having an average particle size of about 0.1 micron diameter and a measured surface area of about to 50 square meters sidual oil having a Saybolt Universal viscosity at 210 F. of about 120 seconds were added. The grease was then heated to 500 F. and allowed to cool. At a temperature below 300 F., 15.5 grams of N,Ndiphenyl paraphenylenediamine dissolved in three times its weight of tricresyl phosphate were added. A short fiber blue grease was Obtained having a dropping point above 500 F. and an ASTM worked penetration of 348.

Table I below shows the high temperature performance properties of the above grease, as measured in the high temperature performance test, together with corresponding data obtained upon a grease prepared from a similar mineral oil base and of substantially the same composition except that sodium myristate was employed as the only soap component.

TABLE I Grease composition, percent The high temperature performance test of the foregoing table is a test for determining the performance characteristics of greases in anti-friction bearings at elevated temperatures and high rotative speeds. The test is carried out as described, for example, in U.S. 2,791,569, column 5, lines 29 to 65. It consists essentially in rotating a test bearing maintained at the test temperature and lubricated with the grease under test at 10,000 rpm until the lubricant fails, which is indicated by the rupture of a low amperage fuse in the driving motor circuit.

As shown by the data given in Table I, the grease representative of the grease compositions of this invention thickened with sodium salts of myristic, pectic and acetic acids in combination with indigo ran for almost per gram, and 1027 grams of a refined paraflinic retwice as long in the high temperature performance test at 350 F. as did the grease thickened with indigo and with sodium myristate as the sole soap component. In contrast to these results, no appreciable improvement in high temperature performance properties were obtained in synthetic oil base greases by replacing sodium myristate employed in conjunction with indigo by the above sodium myristate-sodium pectate-sodium acetate mixture.

Obviously many modifications and variations of the invention, as herein before set forth, may be made without departing from the spirit and scope thereof and therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A lubricating grease consisting essentially of a mineral lubricating oil thickening to a grease consistency by about 5 to 20 percent by weight based on the weight of the composition of indigo in finely divided form and about 5 to 20 percent by weight based on the weight of the composition of a mixture consisting essentially of a soap selected from the class consisting of sodium and lithium soaps of fatty acids containing from 12 to 16 carbon atoms per molecule, a salt selected from the class consisting of sodium and lithium pectates, and a salt selected from the class consisting of sodium and lithium salts of fatty acids containing from 1 to 5 carbon atoms per molecule, compounds of each of the said classes being resent in the said mixture in a mol ratio of from about 1:3 to about 3:1 with compounds of each of the other said classes. I

2. A lubricating grease according to claim 1 wherein the proportion of indigo to the said mixture is from about 1:2 to about 22 1 by weight.

3. A lubricating grease according to claim 1 wherein the mol ration between the compounds of each of the said classes of the said mixture is from about 1:2 to about 2: 1. i

4. A lubricating grease according to claim 1 wherein the said soaps are sodium soaps.

5. A lubricating grease consisting essentially of a mineral lubricating oil thickened to a grease consistency by about 5-15 percent by weight of indigo in finely divided form and about 5-15 percent by weight of a mixture consisting essentially of lithium myristate, lithium pectate and lithium acetate in a mol ratio of about 1-2:1-2:1-2.

6. A lubricating grease consisting essentially of a mineral lubricating oil thickened to a grease consistency by about 5-15 percent by weight of indigo in finely divided form and about 5-15 percent by weight of a mixture consisting essentially of sodium myristate, sodium pectate and sodium acetate in 2 mol ration of about 1-2:1-2:1-2.

7.'A lubricating grease according to claim 6 containing about 0.5-2 percent by weight of N,Ndiphenyl paraphenylenediamine and about 1-5 percent by weight of tricresyl phosphate.

8. A lubricating grease according to claim 6 containing about 0.055.0 percent by weight of an estalide of a high molecular weight hydroxy faty acid having a molecular weight in about the range SOD-1,200.

References Cited in the file of this patent UNITED STATES PATENTS 2,694,683 Morway et a1 Nov. 16, 1954 2,695,878 Entwistle Nov. 30, 1954 2,791,560 Dilworth et al May 7, 1957 2,822,331 Dilworth et al Feb. 4, 1958 UNETE STATES ATENT OFFICE ill;

QE'HHCATE a James Ra Roach ECHGN It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

7 Column 2, line 4L2 for "faty" read fatty column. 4 lines 36 and 52 for -1'ation-"" each occurrence read ratio line 58 ior estalide read estolide line 59 for "faty" read fatty =0 Signed and sealed this 17th day of April 19620 (SEAL) Attest:

ESTON ea JioaNsoN DAVID L. LADD Attesting Officer 7 Commissioner of Patents 

1. A LUBRICATING GREASE CONSISTING ESSENTIALLY OF A MINERAL LUBRICATING OIL THICKENING TO A GREASE CONSISTENCY BY ABOUT 5 TO 20 PERCENT BY WEIGHT BASED ON THE WEIGHT OF THE COMPOSITION OF INDIGO IN FINELY DIVIDED FROM AND ABOUT 5 TO 20 PERCENT BY WEIGHT BASED ON THE WEIGHT OF THE COMPOSITION OF A MIXTURE CONSISTING ESSENTIALLY OF A SOAP SELECTED FROM THE CLASS CONSISTING OF SODIUM AND LITHIUM SOAPS OF FATTY ACIDS CONTAINING FROM 12 TO 16 CARBON ATOMS PER MOLECULE, A SALT SELECTED FROM THE CLASS CONSISTING OF SODIUM AND LITHIUM PECTATES, AND A SALT SELECTED FROM THE CLASS CONSISTING OF SODIUM AND LITHIUM SALTS OF FATTY ACIDS CONTAINING FROM 1 TO 5 CARBON ATOMS PER MOLECULE, COMPOUNDS OF EACH OF THE SAID CLASSES BEING PERCENT IN THE SAID MIXTURE IN A MOL OF FROM ABOUT 1:3 TO ABOUT 3:1 WITH COMPOUNDS OF EACH OF THE OTHER SAID CLASS. 